Die Wirkung von Photooxidantien auf Sommerweizen (Triticum aestivum L. Star)

The effect of short-time fumigation with the peroxidic photooxidants ozone, peroxyacetyl nitrate (PAN), and hydrogen peroxide (H₂O₂) on the gas exchange of wheat leaves was investigated. Two types of experiments are to be distinguished:

1. Fumigation is carried out at atmospheric CO₂ partial pressure (350 μbar) and the assimilation and transpiration rates are followed simultaneously.
2. The alteration of CO₂-response curves by fumigation is determined; from this, characteristic photosynthetic parameters can be calculated.

With this method, statements about the reaction of both photosynthesis as a whole and specific reaction sites within the most important photosynthetic processes are possible. Ozone in concentrations of 260–280 ppb causes a primary perturbation of the photosynthetic apparatus, whereby the carboxylation rate is affected to nearly the same extent as the electron-transport rate.PAN (120 ppb) causes a reduction in the assimilation rate, primarily due to the closing of the stomata. H₂O₂ affects the gas exchange only in concentrations of above 1 ppm, whereby the reduction of the assimilation rate represents an almost pure stomatal effect. All three fumigants cause an increase in the respiration rate, which may point to an activation of detoxification and repair mechanisms.     

Persistent organic pollutants (POPs) in antarctic fish: levels,patterns, changes

Organochlorine compounds were analysed in three fish species of different feeding types from the area of Elephant Island in the Antarctic. In 1996, hexachlorobenzene (HCB) (means: 15-20 ng/g lipid), p,p'-DDE (5-13 ng/g lipid) and mirex (1-7 ng/g lipid) predominated, while PCBs were minor components (PCB 153: 0.4-2 ng/g lipid). Concentration patterns were species-dependent: PCB 180, PCB 153, mirex, nonachlor III, trans-nonachlor and the toxaphene compound B8-1413 were highest in the bottom invertebrate feeder Gobionotothen gibberifrons and lowest in the krill feeder Champsocephalus gunnari. Levels of p,p'-DDE, PCB 138 and heptachloro-1'-methyl-1,2'-bipyrrole (Q1), a natural bioaccumulative product, were highest in the fish feeder Chaenocephalus aceratus, whereas HCB was present in about equal concentrations in all species. Most compounds were taken up preferentially via the benthic food chain, the chlorinated bipyrrole via the pelagic food chain and HCB from the water. In antarctic fish, biomagnification was generally more important than bioconcentration. Between 1987 and 1996, most persistent organic pollutant (POP) levels showed significant increases in the benthos feeder and the fish feeder, while they remained nearly constant or increased less in the krill feeder. Hence, the former species represent indicator species for changing POP levels in Antarctica. Ratios (1996/1987) of average concentrations in G. gibberifrons were: PCB 138 0.7, HCB 0.8, B8-1413 1.5, PCB 180 1.7, PCB 153 1.8, p,p'-DDE 2.0, nonachlor III 2.9, trans-nonachlor 3.3, mirex 6.7. By comparison with trends in the northern hemisphere it is concluded that global distribution of HCB is close to equilibrium. Changing levels of other POPs reflect global redistribution and increasing transfer to antarctic waters probably due to recent usage in the southern hemisphere and climate changes.     

Bromine in waste incineration partitioning and influence on metal volatilisation

INTENTION, GOAL, SCOPE, BACKGROUND: The halogen bromine is far less abundant than chlorine, but it can be found at high concentrations in special materials like flame retarded plastics. The fate and effects of Br in waste incineration are not well understood. It may have similar implications like Cl for the volatilisation of heavy metals and the formation of low volatile organic compounds. Due to its lower oxidation potential, there is a risk of formation of elementary Br2 in the offgas. OBJECTIVE: Co-combustion tests of different types of Br containing plastic waste materials (up to 22%) and MSW in the TAMARA pilot plant for waste incineration were conducted to investigate the Br partitioning and the influence of Br on metal volatilisation. METHODS: The Br inventory of the fuel mix was elevated to approx. 1 wt-%. All input and output mass flows of the furnace have been sampled and the partitioning of Cl, Br, S, and a number of heavy metals, has been calculated on the basis of closed mass balances. RESULTS AND DISCUSSION: Organically-bound Br was typically released to more than 90% into the raw gas. Elementary Br2 was detected at high Br levels. Its presence was always analysed when all SO2 in the raw gas was oxidised to SO3. Br enhances the volatilisation of metals like K, Zn, Cd, Sn, Sb, and Pb out of the fuel bed principally in the same way as Cl. The tests gave strong indication that the promoting influence of the halogens on metal volatilisation is more pronounced than that of the fuel bed temperature. The volatilised metals are condensated on the fly ashes and are discharged along with the filter ashes. CONCLUSIONS: As long as a surplus of SO2 is present in the raw gas no Br2 is formed. Although the halogen induced transfer out of the fuel bed causes high concentrations of volatile metals in the filter ashes, a recovery is not economically feasible for the time being. The volatilisation gives no rise to metal emission problems as long as efficient dedusting is achieved. RECOMMENDATION AND OUTLOOK: If there is a risk of Br2 formation, in wet scrubbing a reducing agent has to be added to the neutral scrubber for efficient abatement. Filter ashes should be disposed of in a way that enables access for recovery in the future. The exact volatilisation characteristics of the various metals have to be studied in future using specifically tailored experiments.     

Cholestyramine enhances fecal elimination of pentachlorophenol in rhesus monkeys

The effect of cholestyramine in the daily diet upon the excretion of pentachlorophenol with the feces was studied in the rhesus monkey. The treatment increased fecal elimination of pentachlorophenol and/or metabolites up to 9- to 14-fold over a six-day period. At the same time urinary excretion was reduced 2- to 6-fold. The data suggest that cholestyramine interrupts the enterhepatic circulation of PCP and/or metabolites thus indicating its possible usefulness in preventing toxicity of PCP that otherwise may occur due to reabsorption of biliary PCP and/or metabolites.